1. Field of the Invention
The present invention relates to a driving apparatus which utilizes an electro-mechanical conversion element such as a piezoelectric element, and more particularly to a driving apparatus for driving an optical member such as a small lens which is installed on a small digital camera, a web camera or a mobile phone with a camera.
2. Description of the Related Art
As the related-art lens driving apparatus which utilizes a piezoelectric element, as is described in the Japanese Patent No. 3358418, there is known a driving apparatus in which a driving member is secured to a piezoelectric element, and a driven member is brought into frictional engagement with the driving member, whereby drive pulses are inputted into the piezoelectric element so as to cause the element to extend and contract to thereby move the driving member backwards and forwards in a straight line, so that the driven member is caused to move relative to the driving member.
This driving apparatus is such as to reduce effects imposed by impact noise produced when the driven member is drastically moved, stopped and reversed by controlling a drive pulse impressing time or drive pulse voltage to change gradually, so that the driving speed changes gradually. For example, when the driving apparatus is started to operate, the traveling speed of the driven member is made to be monitored via information from a detection unit, and in the event that the traveling speed is less than or equal to a constant speed, a drive signal pattern is supplied which increases the speed gradually. Then, when the traveling speed of the driven member reaches the constant speed, the drive signal pattern is switched to a constant drive signal pattern.
However, a driving apparatus like this has a problem that the control of traveling of the driven member is difficult. As shown in FIG. 11, even in the event that the same constant drive signal is imputed into a piezoelectric element 103, there may occur a case where the traveling distance of a driven member 102 differs depending upon the position of the driven member 102 relative to a driving member 101. For example, the driven member 102 travels fast in a central position of the driving member 101, while the traveling of the driven member 102 is delayed in positions lying in end portions of the driving member 101. In this case, since the traveling speed of the driven member 102 changes depending upon the position thereof, the control of traveling of the driven member 102 becomes difficult. In addition, there may occur a case where the traveling speed of the driven member 102 changes depending upon the traveling direction thereof, and in order to control the traveling of the driven member 102 accurately, the traveling of the driven member 102 needs to be desirably controlled in consideration of the change in the traveling speed.